Arc lamp



Feb. 20, 1962 K. MULLER :TAL

ARC LAMP Filed sept. 2s,l 1959 2 Sheets-Sheet 1 l /.......-...........u -na f... 1.... n..

FIC-i2 Feb. 20, 1962 K. MULLER :TAL 3,022,441

ARC LAMP Filed Sept. 23, 1959 2 Sheets-Sheet 2 United States Patent Otiee 3,022,441 Patented Feb. 20, 1952 3,022,441 ARC LAMP Kurt Mller, Stuttgart, and Josef Schleifer, Krumbach,

Schwaben, Germany, assignors to Robert Bosch G.m.b.H., Stuttgart, Germany Fiied Sept. 23, 1959, Ser. No. 841,878 Claims priority, application Germany Sept. 27, 1958 Claims. (Cl. S14- 69) The present invention concerns an arc lamp having a negative and a positive carbon, more particularly a type of arc lamp which is preferab-ly used for movie projectors.

In lamps of this type, it is highly desirable to make sure that the position of the arc remains at all times substantially at one particular point because this is impor-tant for obtaining a permanently uniform illumination of an image which is being projected. On the other hand, it is likewise important and desirable to control the feed of the canbons depending upon the voltage drop across the arc because this voltage drop increases when the arc becomes larger, i.e. when the distance between the tips of the carbons increases. It is 'necessary that this type of control responds to very small voltage Variations.

It has been found that known devices for feeding the carbons, and known control devices therefor, yand even combinations of such known devices, would not yield satisfactory results and would not guarantee a satisfactory operation of the lamp, particularly in the case of projector arc lamps in which the carbons meet at an angle relative to each other.

lt is therefore a main object of this invention to provide for such feed means and control devices therefor which would in an arc lamp avoid the above mentioned difficulties, and overcome the drawbacks'of known devices of this kind.

It is a further object of this invention to provide for an arc lamp of the type set forth,`including feed and control means which are reliable, accurate and nevertheless comparatively simple.

With above objects in view an `arc lamp having a negative and a positive carbon comprises, according to the invention, in combination, first feed means for feeding the negative carbon at a predetermined speed; second feed means for feeding the positive carbon `:alternatively at a predetermined low speed or at a predetermined higher speed; control means for reducing the speed of feed of the negative carbon and simultaneously increasing the speed of feeding the positive carbon from said low speed to said higher speed; and means for operating said control means depending upon the voltage drop across an arc between the carbone and depending upon the position of the burning tip of the positive carbon so `as to operate said control means when the voltage drop across the `arc varies and when the burning tip of the positive carbon moves 'a predetermined distance from its desired predetermined position.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction `and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specic embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a plan view, partly in horizontal section, of an arc lamp according to the invention, the conventional projector mirror being removed;

FIG. 2 is a partly sectional front view of a portion of the arrangement shown in FIG. 1, at a larger scale, the section being taken along line lil-,l1 of FIG. l; and

FIG. 3 is a circuit diagram of the control and operating means of the arc lamp illustrated by FIGS. 1 and 2.

Referring now to FIG. 1, a holder device 2 for a positive carbon 3 and a holder device 4 for a negative carbon 5 are arranged within the housing 1 of 'a projector arc lamp.

The holding device 2 comprises a housing member 6 on top of which guide elements 7 are mounted. These guide elements 7 surround the positive carbon 3 engaging the latter with a certain frictional pressure so that the current fed to the guide elements 7, by means not shown in FIG. l, is transmitted to the positive carbon without undesirable contact resistance.

A support member 8 is mounted on top of the housing 6. This support member 8 contains bearings yand drive elements for three rollers 9, 10 and 1.1 which engage the carbon 3 from three different sides and whose axes are arranged askew with respect to the axis of the carbon, i.e. spaced therefrom and not parallel therewith. When the rollers 9, 10 and 11 are rotated the positive carbon 3 is likewise rotated and simultaneously moved in forward direction through the guide elements 7 in direction towards the point where the arc is formed.

The rollers 9, 16 and 11 are driven by means of a conical gear 12 which meshes with another conical gear 13. The latter is carried by a vertical shaft 14 supported in the housing 6. At the lower end of shaft 14 another conical gear is `attached which is not shown in the drawing, but which meshes with a further conical gear 15. The shaft 16 of the last mentioned gear 15 is supported in a bearing block 17 arranged on the bottom plate of the lamp housing 1.

The holder device 4 of the negative carbon 5 comprises likewise a housing 18. A support member 19 is mounted on this housing and a sliding carrier 20 is 'arranged movable in longitudinal direction on the member 19 by means of guides not shown in the drawing. A clamping member 21 mounted on the sliding member 2t) serves to hold the negative carbon 5.

The supporting member 19 contains a feed screw 22 which cooperates in conventional manner with the sliding member 20 so as to move it in forward direction when the screw or spindle 22 is turned. The rear end of the spindle or screw 22 carries a conical gear 23 which meshes with another conical gear 25 rotatably supported in the housing 18. The sha-ft of the gear 24 carries another conical gear 25 which meshes with a further conical gear 26. The shaft Z7 of the gear 26 is supported in a bearing block 2S mounted on the bottom plate of the lamp housing 1.

Referring now to FIG. 2, the shaft 27 is connected at its outer end by -a cross pin 29 with a cam member Si?. The cam member Si! is surrounded yby a drum-shaped drive member 31. Three balls 32 are located in the space between the members 30 and 31 to serve as coupling elements and are acted upon by springs 33 so as to be forced into the spaces between the curved portions of the cam member 30 and the inner wall surface of the drive member 31. Under the action of the springs 33 the balls 32 engage the just mentioned surfaces of the members 30 and 3l. If then the drive member 31 is rotated in clockwise direction, the rotation of the member 31 is transmitted through the engagement `of the balls 32 to the cam member 30. Consequently, the cam member 3i) constitutes the driven member of an overrunning clutch composed of the above mentioned elements. If the drive member 31 were rotated in counterclockwise direction, then the -bails 32 would move back against the action of the springs 33 as soon `as the cam member 39 would counteract a rotation with a resistance overcoming the force of the springs 33. In such case, the member Sil would not be caused to rotate together with the member 3d.

It is to be understood that the shaft 16 is equipped at its outer end with an overrunning clutch of the same type as described above. Therefore, the so far described portion of FlG. 2 applies also to the drive means for the positive carbon 3, and therefore the numeral 16 is placed in parentheses next to the numeral 27 in FIG. 2.

tach of the overmnning clutches of the shafts 16 and 27 is equipped with control members 34 and 35, respectively, which is connected with shaft members 36 and 37, respectively. These shaft members 36 `and 37 extend through the front wall 38 of the lamp housing 1 and carry at their outer ends control knobs 39, 4t?, respectively. The control members 34, 35 are arranged on their respective shafts 36, 37 coaxially with the pertaining overrunning clutches and carry at their inner face three engagement pics 41 which extend into the spaces between the drive member 31 and the cam member 30 at points which are located on that side of the balls 32 which is remote from the engagement point of the associated spring 33.

If any one of the control knobs 39 or 40 is turned in clockwise direction, then the shoulders 42 of the cam member 3i) will be engaged by the engagement pins 41 so that the cam member together with its shaft 16, 27, respectively, is caused to turn together with the particular knob. If, however, the control knobs are turned counterclockwise, then the balls 32 are engaged by the engagement pins 4l so that the balls 32 are moved out of contact with the `associated engagement surfaces of the members 30 and 31, the springs 33 being somewhat compressed, and the cam member 3d together with the pertaining shaft is again rotated together with the pertaining knob, 1t can lbe seen therefore that by means of the cont-rol knobs 39, itl the feed means and thereby the respeetive carbons can be adjusted and set in either one of the feed directions, backward and forward, by manual operation.

The drive members 31 are interconnected by means of conical gears d3, 4d and a connecting shaft 45 which is supported in bearing blocks d6, 47 mounted on the bottom plate of the lamp housing l.. The shaft 45 carries a third co Aical gear d8 which meshes with a conical gear 49 carried by a shaft The shaft Sil is likewise supported by hearing blocks l, 5.?. mounted on the bottom plate of the lamp housing 1 and carries at its rearward end a further conical gear 53 which meshes with a conical gear S4. This gear 5ft is carried by the shaft S6 of a drive motor S7, however a friction clutch 55 is interposed between the gear 54 and the shaft 56.

The control element 3F is provided at its periphery with a series ot teeth in order to be lockable. A locking' arrangement is provided for cooperating with the series or teeth 58. The locking arrangement comprises a pawl member which is turnably or rockably mounted by means of an axle supported by a bracket 61 mounted on the bottom plate of the lamp housing 1. Normally, the pawl member 59 would be held out of engagement with the teeth 58 by means of `a spring 62 mounted as shown and abuttinfx against a fixed pin in the bracket 61. A pull rod 63 is linked with the outer end of the pawl member 59 and connected with the armature 64 of an electromagnet 65. The free end of the pull rod 63 projecting at the rear end of the electromagnet 65 is provided with a thread 66 `accommodating `an adjustment nut 66 for predetermining the normal position of the pawl member 59 `out of engagement with the teeth SS. Whenever the electromagnet 65 is energized its armature 64 moves into the position shown in FIG. 2. in this case the pawl member 59 engages the series of teeth 58, as shown in FG. 2, and thereby locks the control member 35i in its `actual position. Thereby, a transmission of torque between the drive member 31 and the cam member 3rd is prevented because the balls 32 are prevented from simultaneous engagement with these two members. in this manner, the shaft 27 is likewise arrested and no feeding movement of the negative carbon 5 can take place.

The rear end of the motor shaft 56 carries a fan wheel 67 which conveys air through the inlet tube 68 and blows at least a portion of this air across the bottom of the lamp housing 1 where the above described feed and driving devices are located. A portion of the fan wheel 67 is surrounded by a housing 69 having an opening to which is connected a duet 70. This duct 79 is continued by two branches 71 and 72 of which the tube 71 extends along the housing 6 and ends between the guide elements 7 and a heat protector plate 73. The air delivered through the tube 71 is blown as a coolant in direction toward the carbon 3.

The other tube 72 extends toward the holder device 4 and through the housing 1S where it is branched into two tube elements '74, 75 ending in nozzles 76, 77, respectively, through which the air delivered through the tube 72 is blown in direction toward the arc formed by the tips of the carbons 3 and 5.

When the arc lamp is ignited, the arc is formed between the tips of the negative carbon 5 and positive carbon 3. Some of the rays emanating from the end of the arc at the burning tip of the positive carbon 3 are shown at 78 in FIG. l. These rays are transmitted by a lens 79 mounted laterally in the lamp housing 1 to a mirror 80 and from there to a second mirror 81 from where they are projected across a filter 82 and through a light stop 83 to a photosensitive resistance S4. This photosensitive resistance is mounted together with a number of relays, described below and arranged within a housing 85, on the outside of the lamp housing 1. The relays and the photosensitive resistance are surrounded by a cover 86. Near one end of this cover a number of air inlet openings 87 are provided while the above mentioned duct 68 is connected with the opposite end of the cover 86. Consequently, the air sucked in by the fan wheel 67 travels through the enclosure surrounded by the cover 86 and thereby cools the relays and the photosensitive resistance.

The relays and the entire circuitry of the whole arrangement is described below with reference to FIG. 3. The photosensitive resistor 84 as well as the light stop 83, the lens 79 and the carbons 3 and 5 are shown again diagrammatically in FIG. 3.

The photosensitive resistance 84 is connected in a circuit supplied at 88 with alternating voltage. The coil 90 of a relay 89 is connected in series with the resistor 84. A condensor 91 is connected in parallel with the coil 90. The condensor is so selected that it is capable of compensating the inductivity of the coil when the relay S9 is energized and the soft iron core or armature (not shown) of the coil 9i) is attracted. The relay 89 includes a change-over switch 92 operated by the armature of the coil 90 and cooperating with two stationary contacts 93, 94 which may be alternatively connected by the switch member 92 with the common stationary contact 95.

The negative carbon 5 is connected by a line 96 with the negative terminal 97 of a source of direct current, While the positive carbon 3 is connected by a line 98 with the positive terminal 99 of that source. The coil 161 of a relay lili) is connected in series with the positive carbon 3. A switch member 192 is operated by the coil 161 and is designed to connect a stationary contact 184 with a stationary contact 183 connected with the line 98, whenever the relay 166 is energized. Normally, the member 182 is in open position as shown.

One end of a series resistance is also connected to the line 98, while its opposite end is connected with the one stationary contact 93 and also via a variable resistor 186 with the armature 167 of the above mentioned drive motor 57. The other end of the armature is connected via a resistor 108 with the line 98. One end of a second series resistance 199 is likewise connected with the line 98, while its other end is connected with a line'llt which is connected at one of its ends with the contact 94. The field winding 1.11 of the drive motor 57 is connected between the line 110 and the resistor 108. A tell-tale 112 in series with a resistor 113 is connected between the line 110 and the contact 1014.

The circuit elements and components described above serve in the first place for controlling the feed of the positive carbon 3. The control means for controlling the feed of the negative carbon 5 are all connected between the line 110 and a tap 114 of a potentiometer 120. The voltage available at the tap 114 depends upon the length of operation time and therefore of the general temperature of the whole lamp on account of the following circuit arrangement. A line 1,15 connects the line 96 with the line 98 across two series resistors 116 and 117, in parallel with the carbons 3 and 5. The resistors 116 and 117 are thermistors having opposite temperature coefficients, the resistance of the resistor 116 increasing with increasing temperature while the resistance of the resistor 117 decreases with rising temperature. The series resistors 116, 117 constitute a voltage divider arrangement and are provided with taps 118 and 119, respectively, which are connected with each other across the above mentioned resistor 120 which is a potentiometer having a movable tap 114. The operation of this device will be described further below. The line 1110 is taken to a protective relay 121. 'Ihe coil 122 of this relay is connected between the line 110 and the movable tap 114 via a junction point 127. A variable resistor 123 is connected in parallel with the coil 122. The coil 122 operates a normally closed switch member 12'4 arranged in the line 110, whereby the line 110 is connectedwith the one terminal 125 of the main relay 126. The second terminal 127, identical with the above mentioned junction point, is connected to the movable tap l114. The two ends of a resistor 129 are connected across a non-linear resistor 12S with the two treminals 125 and 127. The right hand end of the resistor 129 is connected Via a rectier 130` with one end of the coil 131 of the main relay 126, while the other end of the coil 131 is connected with a tap 132 of the resistor 129. A compensating condenser 133 is connected in parallel with the coil 131.

A relay switch contact 13S is connected between the tap 132 and a second tap 134 of the resistor 129. The switch device 13S is a part of an auxiliary relay 136 which is equipped with a coil 137 connected between the movable tap 114 and the terminal 125 via the normally open switch member 13S of the main relay 126. The switch member 135 is also normally in open position as shown. The auxiliary relay 136 is additionally equipped with a.second switch member 139, normally closed and connecting the line 98 with the electromagnet 65 which is connected with the line 96 via a resistor 141i.

. As long as the arc lamp is not in operation the coil 101 of the relay lo!) carries no current so that its switch 102 is in open position as shown and therefore all the control devices are without energy. This condition applies also to the period of igniting the lamp. The voltage between the terminals 97 and 99 which are usually terminals of a rectifier device, is during the ignition period higher than during the burning of the lamp. Therefor this excessive voltage is kept from the control devices by means of the switch 102i.

As soon as an karc has been formed the comparatively strong arc current flowing through the coil 1111 causes the switch member 102 to move to closed position. At the rsame time the tell-tale lamp 112l is connected in circuit and lights up.

As long as the positive carbon 3` is in the desired and correct position, the rays emanating from its burning tip do not reach the photosensitive resistor S4. Therefore, the relay 89 remains un-energized and the changeover switch 92 is in the position shown in FG. 3. Con-l sequently, the field winding 111 of the drive motor 57 tis supplied with current via contact 94. Since the arma* ture 167 of the motor 57 is permanently connected via the series resistor 105 with the line 98, the motor 57 starts as soon as the switch 102 is moved to closed position, but the speed of the motor 57 is under these conditions comparatively low.

The rotation of the shaft 56 of the motor 57 results in rotation of the shafts 50 and 45, whereby the conical gears 43 and 44 transmit rotation to the drive members 31 of the two overrunning clutches on the shafts 27 and 16. The shaft 16 is therefore caused to rotate and drives the rolls 9, 10 and 11, whereby the positive carbon 3 is steadily moved forward. The rate of this forward movement or feed is so chosen that it is slightly less than necessary for compensating the consumption of the carbon. However, the overrunning clutch on the shaft 27 is blocked because the electromagnet 65 is steadily energized via the closed switch member 139. Therefore, the negative carbon 5 the consumption of which is substantially slower than that of the positive carbon 31, remains in its actual position. The air conveyed by the fan Wheel 67 cools the relays 89, 100, 121, 126, 136 Ilocated in the housing and also cools the bearings of all driving and driven shafts and is finally blown from the above described ducts and tubings in the marmer and at the points described above.

As soon as the positive carbon 3 has undergone a certalin amount of consumption as illustrated in FIG. 3, the rays emanating from its burning tip reach the photosensitive resistor 84 and render it conductive. Therefore, voltage is applied to the coil of the relay 89 so that this relay becomes energized and moves the change-over switch member 92 into its second position in which the contacts and 93 are connected with each other. Simultaneously with the attraction of the armature of the coil 90, the condenser 9'1 reaches its maximum compensating effect. Therefore, the photosensitive resistor 84 is relieved of reactance current and only a lesser voltage is applied further to the coil 9G.

The change of position of the change-over switch 92 results in shunting or short-circuiting the series resistor 165. Therefore, the armature 107 of the motor 57 is supplied with a higher potential. The held winding 111 of the motor, however, is supplied with current only across the series resistor 109 (the resistor 113` is comparatively large relative to the resistance of the resistor 169). Hereby, the eld of the motor is weakened and the motor rotates faster. Consequently, the positive carhon 3 is quickly moved forward to a position in which no rays from the tip of the positive carbon reach the photosensitive resistor 84 any more. As soon as under these circumstances the resistance of the resistor S4 increases only slightly, the voltage applied to the coil 90 and already reduced by the previously described procedure, decreases further so that the relay 89y is de-en ergized and the change-over switch 92 returns to the iirst position shown in FG'. 3. On account of the above described arrangement, the relay 89 is extremely sensitive and the differential between response voltage and cut-ott voltage is very small.

it can be seen that the whole control arrangement for the feed of the negative carbon 5 operates only if and -when the switch member 92 is in its first position as shown because only under these circumstances the line 11@ carries a suiicient voltage.

The switch 124 remains in closed position as long as the voltage between the terminals 97 and 99 remains within a certain range above and below the normal line voltage or the voltage required for operating the lamp. 1f this voltage increases, then the protective relay 121 is energized suiciently for opening the switch 124 whereby the main relay 126 is disconnected. In this manner, the comparatively sensitive and expensive main relay is protected against damage. The response voltage of the proteetive relay 12,1 can be accurately adjusted by means of the variable resistor 123i.

It can be seen that the relays 121 and 126 do not respond directly to the potential existing between the lines 110 and 96 but to the potential existing between the line 110 and the movable tap 114i. When the arc lamp has just been switched on, voltages appear at the taps 118 and 119 which correspond to the ratio between the pertaining portions of the resistors 116 and 117 in cold condition. In this case, a voltage is available at the tap 114 which ranges between the voltages available at the taps 11S and 119, depending on the setting of the movable tap 114. As long as the resistors 116 and 117 are cold, the voltage available at the tap 114 will not suffice for causing the relays 12,1 and 126 to respond. rl'his entails the advantage that the voltage fiuctuations usually occurring still sometime after the arc has been formed and appearing between the terminals 97 and 99 remain without effect on the control arrangement.

However, when the resistors 116 and 117 have warmed up so that the voltages available at the taps 118, 119 and 114 rise, then these voltages are within the range required for operating the relays. By adjusting the movable tap 114 the response voltage of these relays with respect to the voltage drop across the arc, i.e. with respect to the length of the arc to be maintained by the operation of the relays, may be adjusted to some extent.

The non-linear resistor 128 and the rectifier 1365 serve to permit the coil 131 to respond only to a predetermined voltage, however very sensitively in such case. lf the voltage drop across the arc has risen to a desired and predetermined value, then the main relay 126 becomes energized and closes the switch 138. Hereby, the auxiliary relay 137 is supplied with current and closes the switch 135 whereby a portion of the resistor 129 is short-circuited. The voltage applied to the coil 131 is hereby decreased so that even a small reduction of the voltage drop across the arc would result in de-energizing again the main relay 126.

Whenever the auxiliary relay .137 is energized, the switch 139 is moved to open position. Hereby, the electromagnet 65 is cle-energized and the pawl 59 is disengaged under the action of the spring 62 from the series of teeth 58. Now, the shaft 27 can be rotated via the respective overrunning clutch under the driving action of the shaft 45 and hereby the negative carbon 5 is moved forward. The amount of feed in this case is always very small. As soon as the voltage drop across the arc decreases, the main relay 126 is deeenergized. Hereby, the auxiliary relay 1.37 is likewise again cle-energized, the switch 13% returns to closed position and the feed of the negative carbon is again blocked.

As can be seen from the circuit diagram and the above description, the relays of the whole control arrangement for the negative carbon 5 remains unoperative as long as the relay S9 is energized, i.e. as long as the positive carbon 3 is being fed at a higher speed. Voltage fluctuations across the arc which may occur during the feed remain therefore without any effect on the feeding movement of the negative carbon 5. By the blocking of the feed of the negative carbon 5, this can never be moved forward up to a point where it would contact the holder device of the positive carbon. This could happen if the positive carbon is not replaced in time and entirely consumed. in this case, the relay S9 would remain permanently in energized condition.

The friction clutch S5 on the shaft 56 has only the purpose of preventing mechanical damage if for any reasons both carbons or even portions of the carbon holder devices should have been moved forward so as to contact each other directly.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of arc lamp diifering from the types described above.

While the invention has been illustrated and described as embodied in an arc lamp with automatic feed of the carbons, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. in an arc lamp having a negative and a positive carbon, in combination, first feed means for feeding the negative carbon at a predetermined speed; second feed means for feeding the positive carbon alternatively at a predetermined low speed or at a predetermined higher speed; control means for reducing the speed of feed of the negative carbon and simultaneously increasing the speed of feeding the positive carbon from said low speed to said higher speed; and means for operating said control means depending upon the voltage drop across an arc between the carbons and depending upon the position of the burning tip of the positive carbon so as to operate said control means when the voltage drop across the arc varies and when the burning tip of the positive carbon moves a predetermined distance from its desired predetermined position.

2. in an arc lamp having a negative and a positive carbon, in combination, first feed means for feeding the negative carbon at a predetermined speed; second feed means for feeding the positive carbon alternatively at a predetermined low speed or at a predetermined higher speed; first control means in circuit with the carbons for controlling the power supply to said first and second feed means depending upon the voltage drop across an arc formed between the carbons; second control means connected in series with said first control means for interrupting the feed of the negative carbon and simultaneously increasing the speed of feed of the positive carbon from said low speed to said higher speed; and operating means for operating said second control means and including photosensitive means positioned for scanning the position of the burning tip of the positive carbon so as to operate said second control means depending upon the response of said photosensitive means to radiation from said burning tip o-f the positive carbon when said burning tip moves a predetermined distance from its desired predetermined position.

3. An arc lamp as claimed -in claim 2, wherein said operating means include energizable means in circuit with said photosensitive means, and wherein said second control means includes change-over switch means controlled by said energizable means so as to constitute relay means, said change-over switch means being movable between a first position in which said first feed means is rendered operative and said second feed means is caused to operate at said low speed, and a second position in which said first feed means is rendered inoperative and said second feed means is caused to operate at said higher speed.

4. An arc lamp as claimed in claim 3, comprising drive motor means for driving said feed means and including a field winding and an armature, a first resistor in series with said held winding and a second resistor in series with said armature, said resistors being respectively connected in parallel with said change-over switch means in such a manner that in one position of said change-over switch means said first resistor, and the other position thereof said second resistor is shunted so as to be ineffective.

5. An arc lamp as claimed in claim 3, including a third relay means comprising coil means in circuit with said change-over switch means so as to be energized when said switch means is in its said rst position, normally open switch means operated by said coil means when energized, and means for reducing the voltage across said coil means after the latter has been energized, said third relay means being connected for rendering said first feed means operative when said switch means is moved to closed position.

6. An arc lamp as claimed in claim 5, comprising resistor means connected yin parallel with said coil means of said third relay means, and an auxiliary relay means including electromagnet means in circuit with said switch means of said third relay means, and normally separated contact means operated by said electromagnet means and connected in parallel with at least -a portion of said resistor means for shortcircuiting said portion when said contact means are moved to enga-ge each other, protective relay means including operating coil means connected in series with said resistor means, and a normally closed switch member operated by said operating coil means and connected in series with said coil means for disconnecting the latter when voltage exceeding a predetermined value.

is applied to sa-id third relay means.

7. An arc llamp as claimed in claim 5, comprising voltage divider means connected in parallel with the carbons, said voltage divider means including at least two seriesconnected thermistors having opposite temperature coefficients, respectively, each of said thermistors having a tap, said taps being jointly connected to one terminal of said third relay means for applying to the latter a voltage depending upon the temperature of said thermistors.

8. An arc lamp as claimed in claim 7, wherein a potentiometer is connected between said two taps, and the movable tap of said potentiometer is connected to said one terminal or said third relay means for adjusting the voltage derived from the variable resistance of said thermistors.

9. An arc lamp as claimed in claim 5, comprising resistor means connected in parallel with said coil means of said third means, and an auxiliary relay means including electromagnet means in circuit with said switch means of said third means, and normally separated contact means operated by said electromagnet means and connected in parallel with at least a portion of said resistor means for shortcircuiting said portion when said contact means are moved to engage each other and wherein said auxiliary relay means includes additionally a normally closed contact means operated by said electromagnet means and operatively connected with said iirst feed means for holding the latter in inoperative condition as long as said electromagnet means is un-energized, and for rendering said rst feed means operative when said electromagnet means is energized.

l0. An arc lamp as claimed in claim 4, comprising mechanical transmission means interconnected between said motor means and said first and second feed means, said transmission means including first and second clutch means cooperating with said first and second feed means, respectively, said rst clutch means being under control of said change-over switch means in such a manner that said first feed means are operated by said motor means only when said change-over switch means is in its rst position.

No references cited. 

